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Fig. 1.
The development of morphological left-right asymmetry in theXenopusliver. Cartoon illustrations (A, E) demarcate the positions of the left (L; yellow) and right (R; orange) sides of the developing liver in whole embryos (A; ventral view) and dissected gastrointestinal tracts (E; anterior view). The embryonic midline is indicated by the dashed line in A, and the orientation of the dorsal-ventral axis is indicated by the arrow in E. In situ hybridization was performed at the indicated NF stages (33−44) to detect the liver-specific marker hhex in whole embryos (B-C; NF 33–37, ventral views) or fibrinogen in isolated tracts (F-G; NF 42–44, anterior views). Orange and yellow outlines demarcate the borders of the right and left lobes, respectively. For clarity, the stained specimens are also shown without outlines at higher magnification in B′-C′ and F′-G′; brackets define the extent of each lobe, with the arrow indicating the boundary between left and right lobes. At the earliest stages, the entire hhex-expressing region was outlined (B). Later (~NF 35), when the gall bladder (GB) becomes distinguishable as a separate structure, only the liver lobes themselves were measured (C). The right/left ratio of hhex-expressing tissue area (ventral view) was then quantified at successive stages of development (D; NF 27–39). Ratios close to one (red line) indicate symmetry; left-right asymmetry becomes apparent at NF 33, when the ratio becomes significantly greater than one. At later stages (NF 42–44), the right lobe becomes visibly more elongated than the left (F-G), as quantified by gross length to width ratio (H; NF 46). Asterisks indicate p < 0.05 (*) or p < 0.0001 (**). |
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Fig. 4. Asymmetric expression of pitx2 during Xenopus liver morphogenesis.In situ hybridization was performed on whole NF 35 embryos (A-B) or on serial sections (C-D),probing for the liver specific transcription factor, hhex (A, C), or the LR determinant , pitx2 (B, D). Dotted line in A approximates the section planes shown in C and D. The expression of pitx2is confined to the mesoderm surrounding the left side of the liver diverticulum (arrows in B, D). R=right, L=left. Scale bars= 200 μm. |
